The influence of dietary crude protein concentrations, grain types and arginine:lysine ratios on the performance of broiler chickens.

Abstract

The objective of this study was to investigate the effects of dietary crude protein (CP) concentrations, grain types and arginine:lysine ratios on performance parameters of broiler chickens. The 2×2×2 factorial array of dietary treatments harnessed two CP concentrations (210 and 170g/kg), two feed grains (wheat and sorghum), and two arginine:lysine ratios (104 and 110). Each dietary treatment was offered to 7 replicates of 14 birds per floor pen, a total of 784 off-sex male, Ross 308 broilers, from 14 to 35d post-hatch. The dietary CP reduction compromised weight gain by 10.0% (2078 versus 2310g/bird) as a main effect and FCR by 7.51% (1.474 versus 1.371), subject to an interaction. In a three-way interaction (P=0.008), expanded arginine:lysine ratios improved FCR by 2.30% in 170g/kg CP, sorghum-based diets but compromised FCR by 2.12% in corresponding wheat-based diets. Sorghum was the more suitable feed grain in reduced-CP diets as sorghum generated significant advantages in weight gain of 7.59% (2154 versus 2002g/kg) and FCR of 6.94% (1.421 versus 1.527) in birds offered 170g/kg CP diets. Both dietary CP and feed grain generated significant and divergent impacts in apparent ileal digestibility coefficients for the majority of 16 assessed amino acids. Dietary CP reductions increased non-bound amino acid inclusions (NBAA) in wheat-based diets (48.96 versus 9.80g/kg) to a greater extent than sorghum-based diets (35.3 versus 9.50g/kg) and increasing dietary NBAA inclusions were linearly associated with compromised weight gain (r=-0.834; P<0.001) and FCR (r=0.862; P<0.001). Increasing ratios of free arginine to lysine plasma concentrations were linearly (r=-0.466; P=0.004) related to improvements in FCR. The implications of the observed outcomes are discussed and possible explanations are advanced.